Wireless Communication Device

ABSTRACT

A wireless communication device comprises: an antenna; a radio frequency transceiver, for generating signals for transmission through the antenna, the radio frequency transceiver being connectable to the antenna through a switch; a backscattering block, for generating reflected signals for transmission through the antenna in response to received RF signals, the backscattering block being connectable to the antenna through said switch; and a battery. The switch is controlled by an output voltage of the battery, such that the radio frequency transceiver is connected to the antenna through the switch when the output voltage of the battery exceeds a threshold voltage, and the backscattering block is connected to the antenna through the switch when the output voltage of the battery is below the threshold voltage.

TECHNICAL FIELD

This relates to a wireless communication device, and in particular to abattery-powered device that can communicate using radio frequencysignals, and can act as a backscatter device when the battery is unableto power the radio frequency communication.

BACKGROUND

Battery-powered wireless communication devices are in widespread use.

One class of battery-powered wireless communication devices includesdevices that may be put into service without regular human supervision.For example, the Internet of Things (IoT) may include devices that aredeployed on electrical devices in the home, in order to send reports onthe operation of the devices to a central location. The Internet ofThings may also include devices that include sensors, in order to reportthe sensor data to a central location, for example from a remotelocation.

The IoT devices may be provided at fixed locations or may be intended tobe mobile.

A conventional IoT device contains sensors, a micro-controller toprocess sensor data and perform control tasks, a baseband circuit toencode radio frequency (RF) signals based on the sensor data and todecode received RF signals, and a radio circuit to transmit and receivethe RF signals. A battery is provided to supply power for thesecomponents, and, in general, the radio transceiver requires more powerthan the other components.

During the lifetime of an IoT device, electrical energy is continuouslydrawn from the battery, and so the remaining capacity of the batterywill decrease over time. When its capacity is lower than a certainlevel, the battery cannot supply enough power to keep the radiotransceiver functional. As a result, the IoT device cannot transmit orreceive radio signals, even though the micro-controller and sensors maystill be able to function.

If it is not possible to retrieve these dead IoT devices, both thebattery and the electronics they contain can become an environmentalhazard.

Separately, for example from US2015/0318881, it is known to providedevices that operate by backscattering, that is, by generating andtransmitting reflected signals in response to received RF signals.However, it would be disadvantageous to operate the backscatteringfunction while the radio circuit is operating to transmit and receivethe RF signals.

SUMMARY

According to a first aspect, there is provided a wireless communicationdevice. The wireless communication device comprises an antenna and aradio frequency transceiver, for generating signals for transmissionthrough the antenna. The radio frequency transceiver is connectable tothe antenna through a switch. The wireless communication device furthercomprises a backscattering block, for generating reflected signals fortransmission through the antenna in response to received RF signals. Thebackscattering block is connectable to the antenna through the switch.The wireless communication device further comprises a battery. Theswitch is controlled by an output voltage of the battery, such that theradio frequency transceiver is connected to the antenna through theswitch when the output voltage of the battery exceeds a thresholdvoltage, and the backscattering block is connected to the antennathrough the switch when the output voltage of the battery is below thethreshold voltage.

The switch may comprise first and second transistors, with a conductivepath of the first transistor being connected between the radio frequencytransceiver and the antenna, and a conductive path of the secondtransistor being connected between the backscattering block and theantenna. In that case, the first transistor is turned on and the secondtransistor is turned off when the output voltage of the battery exceedsthe threshold voltage, and the first transistor is turned off and thesecond transistor is turned on when the output voltage of the battery isbelow the threshold voltage.

The wireless communication device may further comprise first and secondoperational amplifiers. In that case, the output voltage of the batterymay be applied to a non-inverting input of the first operationalamplifier, the threshold voltage may be applied to an inverting input ofthe first operational amplifier, an output voltage of the firstoperational amplifier may control the first transistor, the outputvoltage of the first operational amplifier may be applied to aninverting input of the second operational amplifier, a non-invertinginput of the second operational amplifier may be connected to ground,and an output voltage of the second operational amplifier may controlthe second transistor.

The switch may comprise a single-pole, double-throw MEMS switch, whereinthe output voltage of the battery is applied to the switch as a biasvoltage, such that the radio frequency transceiver is connected to theantenna through the switch when the output voltage of the batteryexceeds a threshold voltage, and the backscattering block is connectedto the antenna through the switch when the output voltage of the batteryis below the threshold voltage.

The wireless communication device may further comprise a controller,wherein the controller is configured for modulating signals generated bythe backscattering block based on data for transmission, when thebackscattering block is connected to the antenna through the switch.

The data for transmission may comprise data indicating a status of thedevice.

The data for transmission may comprise data collected by one or moresensor on the device.

The switch may be controlled by hardware in response to an outputvoltage of the battery.

Implementing a backscatter transmitter in a battery-powered wirelesscommunication device has the advantage that the IoT device can belocated when the battery is no longer providing enough power to operatethe radio circuit. A simple hardware circuit is used to control theswitching from the main RF circuit to the backscatter circuit. Thisallows a device that is no longer fully operational to be located andretrieved, without damage to the environment.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show how it may beput into effect, reference will now be made, by way of example, to theaccompanying drawings, in which:—

FIG. 1 illustrates the form of a wireless communication device.

FIG. 2 illustrates a first part of the wireless communication device ofFIG. 1 .

FIG. 3 illustrates in more detail the first part of the wirelesscommunication device of FIG. 1 .

FIG. 4 illustrates in more detail an alternative form of the first partof the wireless communication device of FIG. 1 .

FIG. 5 illustrates a second part of the wireless communication device ofFIG. 1 .

FIG. 6 illustrates in more detail the second part of the wirelesscommunication device of FIG. 1 .

FIG. 7 illustrates an alternative form of the second part of thewireless communication device of FIG. 1 .

DETAILED DESCRIPTION

FIG. 1 is a block diagram illustrating a wireless communication device10. In one example, the wireless communication device is an Internet ofThings (IoT) device.

The device 10 includes one or more sensor 12, and a micro-controller 14.The micro-controller 14 is used to collect data from the sensor(s) 12.The micro-controller 14 is also used as a control unit in the IoTdevice.

Sensor data received by the micro-controller 14 from the sensor(s) 12can be sent to digital baseband circuitry 16, and then to a radiofrequency (RF) transceiver circuit 18. The RF transceiver circuit may beconnected to an antenna 20 so that the sensor data can be transmittedover a wireless communications interface, for example to a centraldevice that receives sensor data from multiple IoT devices. Signalsreceived by the antenna 20 can also be passed to the RF transceivercircuit 18, and then to the baseband circuitry 16 and themicro-controller 14.

The digital baseband circuitry 16 and RF transceiver 18 can beconfigured to operate using any suitable form of radio communication,including any desired form of radio access technology, such as cellulartechnology, for example as standardised by 3GPP, WiFi, or a short-rangewireless technology such as Bluetooth.

The circuitry, including the micro-controller 14, the digital basebandcircuitry 16, and the RF transceiver circuit 18, is powered by a battery22.

The device 10 also includes a backscattering block 24, which may also beconnected to the antenna 20.

As discussed in more detail below, an antenna switch 26 is connected tothe antenna 20, such that only one of the RF transceiver circuit 18 andthe backscattering block 24 is connected to the antenna 20 at any onetime.

More specifically, a power management block 28, including a batteryvoltage monitor 30, is connected to the battery 22, in order to monitoran output voltage of the battery 22. The power management block 28 isconnected to a switch controller 32, in order to control the operationof the antenna switch 26.

When the output voltage of the battery 22 remains above a thresholdlevel, the switch controller 32 controls the operation of the antennaswitch 26 so that the RF transceiver circuit 18 is connected to theantenna 20. The threshold voltage level may be set such that itcorresponds to a voltage that is sufficient for the operation of themicro-controller 14, the digital baseband circuitry 16, and the RFtransceiver circuit 18. As mentioned above, it is usually the RFtransceiver circuit 18 that requires the most power. However, when theoutput voltage of the battery 22 falls below the threshold level,meaning that the RF transceiver circuit 18 can no longer operate asintended, the switch controller 32 controls the operation of the antennaswitch 26 so that the backscattering block 24 is connected to theantenna 20.

FIG. 2 shows in more detail the general form of the backscattering block24.

The backscattering block 24 operates by detecting a radio frequencywave, which may for example be transmitted by a hub device, andreflecting a fraction of the detected wave back to the hub. The wavereflection occurs due to an intentional mismatch between the antennaimpedance and a load impedance of the backscattering block.

Varying the load impedance varies the property of reflection, and so thereflected wave may be modulated with data to be transmitted.

This is shown in general terms in FIG. 4 , which shows thebackscattering block 24 including an impedance 40, the impedance valueof which may be varied under the control of the micro-controller 14.

Thus, by switching the value of the load impedance 40 between differentvalues, data can be modulated onto the reflected signal.

In other embodiments, the backscattering block 24 may modulate the datawith a subcarrier to shift the incoming signals by the frequency of thesubcarrier and backscatter the frequency-shifted signal.

FIG. 3 shows a more specific example of the general structure shown inFIG. 2 . In FIG. 3 , two impedances 42, 44, with impedance values Z1 andZ2, are connected in parallel between a switch 46 and ground. The switchis controlled by the micro-controller 14.

Thus, when the micro-controller 14 controls the switch 46 so that theimpedance 42 is connected to the antenna switch 26, the load impedanceof the backscattering block 24 has the impedance value Z1. When themicro-controller 14 controls the switch 46 so that the impedance 44 isconnected to the antenna switch 26, the load impedance of thebackscattering block 24 has the impedance value Z2.

FIG. 4 shows an alternative more specific example of the generalstructure shown in FIG. 2 . In FIG. 4 , the backscattering circuit 50takes the form of a field effect transistor (FET) 52 connected betweenthe antenna switch 26 and ground. The gate of the FET 52 is connected toreceive a data signal generated by the micro-controller 14.

Thus, when the micro-controller 14 generates a data 1, the FET 52 isturned ON, and the antenna load impedance of the backscattering block 24is close to zero. When the micro-controller 14 generates a data 0, theFET 52 is turned OFF, and the antenna load impedance of thebackscattering block 24 is effectively infinite.

Thus, in these embodiments, the load impedance presented by thebackscattering block can be controlled by the micro-controller 14,allowing data to be contained within the reflected signals.

As mentioned above, the antenna switch 26 is connected to the antenna20, such that only one of the RF transceiver circuit 18 and thebackscattering block 24 is connected to the antenna 20 at any one time.More specifically, the power management block 28 is connected to aswitch controller 32, in order to control the operation of the antennaswitch 26. When the output voltage of the battery 22 remains above athreshold level, the switch controller 32 controls the operation of theantenna switch 26 so that the RF transceiver circuit 18 is connected tothe antenna 20, but when the output voltage of the battery 22 fallsbelow the threshold level, the switch controller 32 controls theoperation of the antenna switch 26 so that the backscattering block 24is connected to the antenna 20.

FIG. 5 shows a first embodiment of an antenna switch 26, connected sothat either the main RF circuitry 18 or the backscattering block 24 canbe connected to the antenna 20.

In this example, the antenna switch 26 includes a single pole doublethrow (SP2T) RF switch 60, with a first terminal RF1 connected to the RFcircuitry 18, a second terminal RF2 connected to the backscatteringblock 24, and a third terminal RFC connected to the antenna 20.

In this embodiment, a hardware circuit containing two operationalamplifiers (op-amps) 62, 64 acts as the antenna switch controller 32.The battery voltage VBAT acts as an input to the switch controller 32.

More specifically, the battery voltage VBAT is provided as an input tothe non-inverting input terminal of a first op-amp 62, while a thresholdvoltage VBAT_L is provided as an input to the inverting input terminalof the first op-amp 62. The output of the first op-amp 62 is provided asa first control input VC1 to the switch controller 32, and is alsoprovided as an input to the inverting input terminal of the secondop-amp 64. The non-inverting input terminal of the second op-amp 64 isconnected to ground. The output of the second op-amp 64 is provided as asecond control input VC2 to the switch controller 32.

Thus, when the battery voltage VBAT is higher than the threshold voltageVBAT_L, the output of the first op-amp 62 is HIGH, that is VC1 is HIGH.The second op-amp 64 acts as an inverter, and so its output is LOW, thatis VC2 is LOW. Conversely, when the battery voltage VBAT is lower thanthe threshold voltage VBAT_L, the output of the first op-amp 62 is LOW,that is VC1 is LOW. The second op-amp 64 acts as an inverter, and so itsoutput is HIGH, that is VC2 is HIGH.

FIG. 6 shows in more detail one possible form of the SP2T switch 60.Specifically, in this embodiment, the switch 60 comprises a first FET70, with its conductive path connected between the first terminal RF1and the third terminal RFC of the switch 60, and its gate terminalcontrolled by the first control input voltage VC1. The switch 60 alsocomprises a second FET 72, with its conductive path connected betweenthe second terminal RF2 and the third terminal RFC of the switch 60, andits gate terminal controlled by the second control input voltage VC2.

FIG. 6 shows the situation where VBAT is higher than the thresholdvoltage VBAT_L, and so VC1 is HIGH and VC2 is LOW. This means that thefirst FET 70 has a small resistance and the second FET 72 has a largeresistance, and hence that the path between the first terminal RF1 andthe third terminal RFC of the switch 60 is turned ON, and the pathbetween the second terminal RF2 and the third terminal RFC is turnedOFF.

Thus, the RF circuitry 18 is connected to the antenna 20 while thebattery voltage is high enough to allow the RF circuitry to operatesuccessfully.

Conversely, when VBAT is lower than the threshold voltage VBAT_L, VC1 isLOW and VC2 is HIGH. This means that the first FET 70 has a largeresistance and the second FET 72 has a small resistance, and hence thatthe path between the first terminal RF1 and the third terminal RFC ofthe switch 60 is turned OFF, and the path between the second terminalRF2 and the third terminal RFC is turned ON.

Thus, the backscattering block 24 is connected to the antenna 20 whenthe battery voltage is no longer high enough to allow the RF circuitryto operate successfully.

The following table shows the logical operation of the switch 60.

VC1 VC2 RFC-RF1 RFC-RF2 High Low ON OFF Low High OFF ON

FIG. 7 shows a second embodiment of an antenna switch 26, againconnected so that either the main RF circuitry 18 or the backscatteringblock 24 can be connected to the antenna 20.

In this example, the antenna switch 26 includes a SP2Tmicroelectromechanical system (MEMS) switch 80, with a first terminalRF1 connected to the RF circuitry 18, a second terminal RF2 connected tothe backscattering block 24, and a third terminal RFC connected to theantenna 20. For example, the SP2T MEMS switch 80 may be as disclosed in“SPDT RF MEMS Switch Using A Single Bias Voltage And Based On DualSeries And Shunt Capacitive MEMS Switches”, T. Ketterl and T. Weller,2005 European Microwave Conference, or in “A Compact DC—20 GHz SPDTSwitch Circuit Using Lateral RF MEMS Switches”, M. Tang, A. Liu, A.Agarwal, 2005 Asia-Pacific Microwave Conference Proceedings.

In this example, the antenna switch is controlled directly from thebattery voltage VBAT, although in other embodiments a voltage boostcircuit (for example the MAX1606 step-up DC-DC converter) may be neededto convert the battery voltage to the bias voltage required by the MEMSswitch.

In normal operation mode, with VBAT higher than a threshold (for example0.5V), the MEMS switch 80 is in the ON state, and so the path betweenthe first terminal RF1 and the third terminal RFC of the switch 80 isturned ON, and the path between the second terminal RF2 and the thirdterminal RFC is turned OFF. Thus, the RF circuitry 18 is connected tothe antenna 20.

When VBAT falls lower than the threshold, the bias voltage is no longersufficient to keep the MEMS switch 80 in the ON state. As a result, theconnection to the antenna is switched from the RF transceiver circuitry18 to the backscattering block 24.

Thus, the antenna switch operates so that the radio frequencytransceiver is connected to the antenna through the switch when theoutput voltage of the battery exceeds a threshold voltage, and thebackscattering block is connected to the antenna through the switch whenthe output voltage of the battery is below the threshold voltage.

When the backscattering block 24 is connected to the antenna 20, themicro-controller 14 can modulate the backscattered signal by some data.

For example, in some situations the micro-controller 14 can continue toobtain sensor data and send the data via the modulated backscatteredsignal, or can transmit data that the RF circuitry was unable totransmit.

As another example, the micro-controller can modulate the backscatteredsignal with an error code to report the reason why the RF circuitry isnot connected, for example an error code corresponding to a low batteryvoltage.

As another example, the micro-controller can modulate the backscatteredsignal with information relating to the location of the device, allowingthe device to be retrieved if required.

The IoT device can report information about any aspect of its status,for example its battery voltage, to an access point by means of thebackscattered signal.

There is thus described a battery-powered device where a main RF circuitis used to transmit and/or receive data. An RF backscattering circuit isdisconnected when the main RF circuit is functional but, once the deviceis unable to function normally because of a low battery level, thebackscatter transmitter is enabled by hardware.

The embodiments herein are not limited to the above described preferredembodiments. Various alternatives, modifications and equivalents may beused. Therefore, the above embodiments should not be taken as limitingthe scope of the invention, which is defined by the appended claims.

1. A wireless communication device, comprising: an antenna; a radiofrequency transceiver, for generating signals for transmission throughthe antenna, the radio frequency transceiver being connectable to theantenna through a switch; a backscattering block, for generatingreflected signals for transmission through the antenna in response toreceived RF signals, the backscattering block being connectable to theantenna through said switch; and a battery, wherein the switch iscontrolled by an output voltage of the battery, such that the radiofrequency transceiver is connected to the antenna through the switchwhen the output voltage of the battery exceeds a threshold voltage, andthe backscattering block is connected to the antenna through the switchwhen the output voltage of the battery is below the threshold voltage.2. A wireless communication device according to claim 1, wherein theswitch comprises first and second transistors, with a conductive path ofthe first transistor being connected between the radio frequencytransceiver and the antenna, and a conductive path of the secondtransistor being connected between the backscattering block and theantenna, wherein the first transistor is turned on and the secondtransistor is turned off when the output voltage of the battery exceedsthe threshold voltage, and wherein the first transistor is turned offand the second transistor is turned on when the output voltage of thebattery is below the threshold voltage.
 3. A wireless communicationdevice according to claim 2, further comprising first and secondoperational amplifiers, wherein the output voltage of the battery isapplied to a non-inverting input of the first operational amplifier,wherein the threshold voltage is applied to an inverting input of thefirst operational amplifier, and wherein an output voltage of the firstoperational amplifier controls the first transistor, and wherein theoutput voltage of the first operational amplifier is applied to aninverting input of the second operational amplifier, wherein anon-inverting input of the second operational amplifier is connected toground, and wherein an output voltage of the second operationalamplifier controls the second transistor.
 4. A wireless communicationdevice according to claim 1, wherein the switch comprises a single-pole,double-throw MEMS switch, wherein the output voltage of the battery isapplied to the switch as a bias voltage, such that the radio frequencytransceiver is connected to the antenna through the switch when theoutput voltage of the battery exceeds a threshold voltage, and thebackscattering block is connected to the antenna through the switch whenthe output voltage of the battery is below the threshold voltage.
 5. Awireless communication device according to claim 1, further comprising acontroller, wherein the controller is configured for modulating signalsgenerated by the backscattering block based on data for transmission,when the backscattering block is connected to the antenna through theswitch.
 6. A wireless communication device according to claim 5, whereinthe data for transmission comprises data indicating a status of thedevice.
 7. A wireless communication device according to claim 5, whereinthe data for transmission comprises data collected by one or more sensoron the device.
 8. A wireless communication device according to claim 1,wherein the switch is controlled by hardware in response to an outputvoltage of the battery.